Display screen or portion thereof with a graphical user interface



The single FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing our new design.

The grayscale shading within the solid line rectangular shapes indicates contrasts in appearance. The outermost broken line showing the display screen or portion thereof and all other broken lines showing portions of the graphical user interface are included for the purpose of illustrating portions of the article and form no part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 